no ... but you can look
the label on the back will give you the power rating
a pc (crt or lcd) ... 120 - 500+ watts depending on all sorts of factors - big games machines eat lekky.
and it's not going to be on a label either ... but the PSU rating will give an idea if it's a guzzler (320w - 1Kw are common)
your telly could be 10-180+ watt - lcd plasma
depending on all sorts of factors
the only way to tell is look at the label
one of these will tell you exactly
http://www.maplin.co.uk/Module.aspx?moduleno=3 8343